ages = {
    'Tom': 18,
    'Jack': 19,
    'Alex': 17
}
print(ages)
print("----------------------------------增删改查")

ages["张三"] = 20
ages.setdefault("李四", 21)

ages.pop("Alex")
del ages["Jack"]

ages["Tom"] = 22
print(ages)

print(ages["李四"])

ages.clear()

